A method for opening holes in a tin bead prevention printing template and a tin bead prevention printing template

Abstract

The application provides a method for opening holes in a printing template for preventing tin beads and a printing template for preventing tin beads. The method comprises the following steps: obtaining each solder end area of a QFN device and each pad area of a PCB; determining the interval between each two oppositely arranged solder ends; determining the interval between each two pads; determining the length by which the inner side end of each pad extends beyond the inner side end of the corresponding solder end; determining the length by which the inner side end of each pad extends beyond the inner side end of the corresponding hole on the printing template and the length by which the outer side end of each hole extends beyond the outer side end of the corresponding pad; determining the inner side end position and the outer side end position of the holes on the printing template; determining the upper side end position and the lower side end position of the holes on the printing template according to the center interval of each two adjacent pads, and determining the hole area of the printing template according to the inner side end position, the outer side end position, the upper side end position and the lower side end position of the holes on the printing template. The application can solve the technical problem of tin bead residues generated at the bottom of the QFN device after soldering.

Description

Technical Field

[0001] This invention relates to the field of electronic assembly technology, and in particular to a method for opening holes in an anti-solder ball printing template and an anti-solder ball printing template. Background Technology

[0002] With the trend towards multifunctionality and miniaturization in electronic products, components are becoming increasingly miniaturized and highly integrated. QFN (Quad Flat Non-lead) devices are square, flat, leadless packages with conductive solder terminals around the bottom perimeter for electrical connection. These devices offer advantages such as small package size, high integration, and high power. However, due to the small lead pitch and invisible solder terminals, after soldering and connection to the pads to form the bottom solder joint, excess solder balls easily accumulate at the bottom. These balls can be located between the solder terminals or between the solder terminal and the heatsink, reducing electrical insulation clearance and potentially causing short circuits. Because the bottom solder joints are hidden, solder balls cannot be removed by peeling or cleaning; therefore, solving the problem of solder ball formation is a crucial issue that urgently needs to be addressed.

[0003] Before soldering, the stencil has corresponding openings. The solder paste is filled into the openings of the stencil using the squeegee of the printing machine. After the stencil is removed from the PCB, solder paste with a fixed shape and thickness is left on the PCB pads.

[0004] To avoid the aforementioned issue of excess solder balls at the bottom, existing technologies offer two methods:

[0005] I. Currently, the thickness of the printing stencil used for printed products PCBs is 0.13mm, 0.12mm, and 0.1mm. The amount of solder on QFN devices can be controlled by changing the thickness of the printing stencil. However, due to the large differences in the spacing between devices on the product, the requirements for the thickness of the printing stencil are not the same. Therefore, reducing the thickness of the printing stencil as a whole can easily cause solder joint defects in other devices due to insufficient solder paste.

[0006] Second, localized solder volume control can currently be achieved through a stepped stencil design. However, due to the high device density, the gradient of the stepped stencil is difficult to achieve, and it also increases the difficulty in controlling the squeegee pressure of the printing press, as well as the cost of the stencil. Summary of the Invention

[0007] This invention provides a method for opening holes in an anti-solder ball printing template and an anti-solder ball printing template, which can solve the technical problem of excess solder balls generated at the bottom of QFN devices after soldering.

[0008] According to one aspect of the present invention, a method for opening a stencil to prevent solder balling is provided, the method comprising:

[0009] Obtain each solder terminal area of ​​the QFN device and each pad area of ​​the PCB, and set each solder terminal area to correspond one-to-one with each pad area;

[0010] The spacing between every two oppositely positioned solder terminals that are not on the same side is determined based on each solder terminal region of the QFN device;

[0011] Determine the spacing between two pads corresponding to every two oppositely positioned solder terminals based on each pad area of ​​the PCB;

[0012] Place the QFN device on the PCB so that each solder terminal area corresponds to each pad area. Determine the length of the inner end of each pad extending beyond the inner end of the corresponding solder terminal based on the spacing between every two relatively set solder terminals and the spacing between every two relatively set pads.

[0013] The length of the inner end of each pad extending beyond the inner end of the corresponding solder end is determined based on the length of the inner end of each pad extending beyond the inner end of the corresponding hole on the printing template, and the length of the outer end of each hole extending beyond the outer end of the corresponding pad.

[0014] The positions of the inner and outer ends of the openings on the printing template are determined based on the length of the inner end of each pad extending beyond the inner end of the corresponding opening on the printing template and the length of the outer end of each opening extending beyond the outer end of the corresponding pad.

[0015] The upper and lower ends of the openings on the stencil are determined based on the center-to-center distance between any two adjacent pads. The opening area of ​​the stencil is then determined based on the inner, outer, upper, and lower ends of the openings.

[0016] Preferably, the length of the inner end of each pad extending beyond the inner end of the corresponding solder terminal is determined by the following formula:

[0017] m = (aA) / 2;

[0018] In the formula, m is the length of the inner end of each pad extending beyond the inner end of the corresponding solder end, A is the spacing between every two oppositely positioned pads, a is the spacing between every two oppositely positioned solder ends, and m > 0.

[0019] Preferably, the length of the inner end of each pad extending beyond the inner end of the corresponding opening on the printing stencil is determined by the following formula:

[0020] X = m + Δt;

[0021] Where 0 ≤ Δt < 0.1 mm;

[0022] In the formula, X is the length of the inner end of each pad extending beyond the inner end of the corresponding opening on the printing stencil.

[0023] Preferably, the length by which the outer end of each opening extends beyond the outer end of the corresponding pad satisfies the following formula:

[0024] 0≤X 1≤X;

[0025] In the formula, X1 is the length of the outer end of each opening extending beyond the outer end of the corresponding pad, and X is the length of the inner end of each pad extending beyond the inner end of the corresponding opening on the printing stencil.

[0026] Preferably, obtaining each solder joint area of ​​the QFN device includes: obtaining each solder joint area of ​​the QFN device from the QFN device datasheet.

[0027] Preferably, obtaining each pad area of ​​the PCB includes: obtaining each pad area of ​​the PCB from the PCB file.

[0028] Preferably, the shape of the opening is adapted to the shape of the pad.

[0029] According to another aspect of the present invention, a solder ball prevention printing template is provided, the printing template including an opening, the opening being obtained by any of the methods described above.

[0030] Preferably, the shape of the opening is adapted to the shape of the pad.

[0031] Preferably, the thickness of the printing template is greater than 0.1 mm.

[0032] By applying the technical solution of this invention, the actual soldering area of ​​the pad is determined based on the relative position of the pad and the solder tip. Then, holes are made in the corresponding area of ​​the printed circuit board (PCB) according to the actual soldering area. That is, by changing the position and shape of the holes in the PCB, the problem of excess solder balls after soldering can be solved without reducing the thickness of the PCB or reducing the amount of solder. Furthermore, this invention makes targeted holes based on the pad positions of each QFN device, thus avoiding an increase in the overall missing solder ratio. The technical solution of this invention achieves the effect of locally maintaining the amount of solder paste and avoiding excess solder balls by only changing the position and shape of the holes on a two-dimensional plane. Compared with the existing three-dimensional stepped PCB design, it is simpler to design, easier to implement, and lower in cost. Attached Figure Description

[0033] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of the invention and illustrate the principles of the invention together with the textual description. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0034] Figure 1 A flowchart of a method for creating openings in a printing stencil to prevent solder beads, according to an embodiment of the present invention, is shown.

[0035] Figure 2 A schematic diagram of the structure of a printing template provided according to an embodiment of the present invention is shown;

[0036] Figure 3 A schematic diagram of the QFN device is shown.

[0037] Figure 4 A schematic diagram of the PCB structure is shown;

[0038] Figure 5 A schematic diagram of a QFN device mounted on a PCB is shown.

[0039] Figure 6 The diagram shows the opening of the printing stencil according to an embodiment of the present invention, and the solder terminals of the QFN device are aligned with the solder pads of the PCB.

[0040] The above figures include the following reference numerals:

[0041] 10. Printing template; 11. Opening; 111. Inner end of opening; 112. Outer end of opening; 113. Upper end of opening; 114. Lower end of opening; 20. QFN device; 21. Solder terminal; 211. Inner end of solder terminal; 212. Upper end of solder terminal; 213. Lower end of solder terminal; 30. PCB; 31. Solder pad; 311. Inner end of solder pad; 312. Outer end of solder pad. Detailed Implementation

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0045] like Figure 1 As shown, the present invention provides a method for opening holes in a printing stencil to prevent solder beads, the method comprising:

[0046] S10. Obtain each solder terminal 21 area of ​​the QFN device 20 and each pad 31 area of ​​the PCB 30, and set each solder terminal 21 area to correspond one-to-one with each pad 31 area;

[0047] S20. Determine the spacing between every two oppositely arranged solder terminals 21 that are not on the same side, based on the region of each solder terminal 21 of the QFN device 20.

[0048] S30. Determine the spacing between two pads 31 corresponding to every two oppositely positioned solder ends 21 according to each pad 31 area of ​​PCB 30;

[0049] S40. Place the QFN device 20 on the PCB 30 so that each solder terminal 21 area corresponds to each pad 31 area. Determine the length of the inner end 311 of each pad extending beyond the inner end 211 of the corresponding solder terminal based on the spacing between each pair of oppositely arranged solder terminals 21 and the spacing between each pair of oppositely arranged pads 31.

[0050] S50. Determine the length of the inner end 311 of each pad extending out of the inner end 211 of the corresponding solder end, and the length of the outer end 112 of each opening extending out of the outer end 312 of the corresponding solder pad, based on the length of the inner end 311 of each pad extending out of the inner end 211 of the corresponding solder end.

[0051] S60. Determine the position of the inner end 111 and the outer end position of the opening on the printing template 10 based on the length of the inner end 311 of each pad extending out of the inner end 111 of the corresponding opening on the printing template 10 and the length of the outer end 112 of each opening extending out of the outer end 312 of the corresponding pad.

[0052] S70. Determine the position of the upper end 113 and the lower end 114 of the opening on the printing template 10 according to the center distance D between two adjacent pads 31, and determine the opening area 11 of the printing template 10 according to the inner end position, outer end position, upper end position and lower end position of the opening on the printing template.

[0053] This invention determines the actual soldering area of ​​the pad 31 based on the relative position of the pad 31 and the solder tip 21. Then, based on the actual soldering area of ​​the pad 31, holes 11 are made in the corresponding area of ​​the printed circuit board 10. That is, by changing the position and shape of the holes 11 in the printed circuit board 10, the problem of excess solder balls after soldering can be solved without reducing the thickness of the printed circuit board 10, without reducing the amount of solder. Simultaneously, this invention makes targeted holes 11 based on the position of the pads 31 of each QFN device 20, without increasing the overall missing solder ratio. The technical solution of this invention only changes the position and shape of the holes 11 on a two-dimensional plane to achieve the effect of locally maintaining the amount of solder paste and avoiding excess solder balls. Compared with the existing three-dimensional stepped printed circuit board 10, the design is simpler, easier to implement, and lower in cost.

[0054] In this embodiment, the shape of the aperture 11 is adapted to the shape of the pad 31. Specifically, the shape of the aperture 11 is the same as the shape of the pad 31, but the position and size of the aperture 11 are different from the position and size of the pad 31, such as... Figure 2 and Figure 3 As shown.

[0055] In this embodiment, five solder terminals 21 are provided on each side of the QFN device 20, such as... Figure 3 As shown; correspondingly, each side of the PCB30 is provided with 5 pads 31 that correspond one-to-one with the solder terminals 21, as follows. Figure 4 As shown; correspondingly, each side of the printing stencil 10 is provided with 5 openings 11 that correspond one-to-one with the pads 31, such as Figure 2 As shown.

[0056] According to one embodiment of the present invention, in S10, obtaining each solder terminal 21 region of the QFN device 20 includes: obtaining each solder terminal 21 region of the QFN device 20 through the QFN device datasheet. Obtaining each pad 31 region of the PCB 30 includes: obtaining each pad 31 region of the PCB 30 through the PCB file.

[0057] like Figure 5 As shown, according to one embodiment of the present invention, in S40 of the present invention, the length of the inner end 311 of each pad extending beyond the inner end 211 of the corresponding solder end is determined by the following formula:

[0058] m = (aA) / 2;

[0059] In the formula, m is the length of the inner end of each pad extending beyond the inner end of the corresponding solder end, A is the spacing between every two oppositely positioned pads, a is the spacing between every two oppositely positioned solder ends, and m > 0.

[0060] like Figure 6 As shown, according to an embodiment of the present invention, the length of the inner end 311 of each pad extending beyond the inner end 111 of the corresponding opening on the printing template 10 is determined by the following formula:

[0061] X = m + Δt;

[0062] Where 0 ≤ Δt < 0.1 mm;

[0063] In the formula, X is the length of the inner end of each pad extending beyond the inner end of the corresponding opening on the printing stencil.

[0064] Furthermore, when 0 < Δt < 0.1 mm, the generation of excess solder beads can be further avoided.

[0065] According to one embodiment of the present invention, the length by which the outer end 112 of each opening extends beyond the outer end 312 of the corresponding pad satisfies the following formula:

[0066] 0≤X 1≤X;

[0067] In the formula, X1 is the length of the outer end of each opening extending beyond the outer end of the corresponding pad, and X is the length of the inner end of each pad extending beyond the inner end of the corresponding opening on the printing stencil.

[0068] Furthermore, when X1 = X, that is, when the length of the pad 31 is the same as the length of the opening 11, it can be further ensured that the amount of solder paste is sufficient, and soldering defects caused by insufficient amount of solder paste can be avoided.

[0069] In this embodiment, if the center-to-center distance D between any two adjacent pads 31 is 0.5 mm, then the distance between the upper end 113 and the lower end 114 of the opening on the printed template 10 is 0.23 mm. Specifically, this can be determined based on existing soldering strategies.

[0070] After obtaining the printing template 10 with the completed opening 11 using the above method, the printing template 10 with the completed opening 11 is covered on the corresponding position of the PCB 30 to complete the printing of solder paste, and then soldering is performed to avoid the generation of excess solder balls after soldering.

[0071] According to another aspect of the present invention, a solder ball prevention printing template is provided, the printing template 10 including an opening 11, the opening 11 being obtained by any of the methods described above.

[0072] According to one embodiment of the present invention, the shape of the opening 11 is adapted to the shape of the pad 31. Specifically, the shape of the opening 11 is the same as the shape of the pad 31, but the position and size of the opening 11 are different from the position and size of the pad 31, such as... Figure 2 and Figure 3 As shown.

[0073] According to one embodiment of the present invention, the thickness of the printing template 10 is greater than 0.1 mm to avoid welding defects caused by insufficient solder paste.

[0074] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0075] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of opening a printing stencil against tin beads, characterized in that, The method comprises: obtaining each solder end region of the QFN device and each pad region of the PCB, each solder end region being arranged one-to-one with each pad region; determining the interval between each two oppositely arranged solder ends not on the same side according to each solder end region of the QFN device; determining the interval between each two pads corresponding to each two oppositely arranged solder ends according to each pad region of the PCB; placing the QFN device on the PCB so that each solder end region corresponds to each pad region, and determining the length of the inner side end of each pad extending out of the inner side end of the corresponding solder end according to the interval between each two oppositely arranged solder ends and the interval between each two oppositely arranged pads; determining the length of the inner side end of each pad extending out of the inner side end of the corresponding opening on the printing template and the length of the outer side end of each opening extending out of the outer side end of the corresponding pad according to the length of the inner side end of each pad extending out of the inner side end of the corresponding solder end; determining the inner side end position and the outer side end position of the opening on the printing template according to the length of the inner side end of each pad extending out of the inner side end of the corresponding opening on the printing template and the length of the outer side end of each opening extending out of the outer side end of the corresponding pad; determining the upper side end position and the lower side end position of the opening on the printing template according to the center interval of each two adjacent pads, and determining the opening region of the printing template according to the inner side end position, the outer side end position, the upper side end position and the lower side end position of the opening on the printing template; the length of the inner side end of each pad extending out of the inner side end of the corresponding solder end is determined by the following formula: m=(a-A) / 2; wherein m is the length of the inner side end of each pad extending out of the inner side end of the corresponding solder end, A is the interval between each two oppositely arranged pads, a is the interval between each two oppositely arranged solder ends, and m>0, the length of the inner side end of each pad extending out of the inner side end of the corresponding opening on the printing template is determined by the following formula: X=m+Δt; wherein 0≤Δt<0.1mm; wherein X is the length of the inner side end of each pad extending out of the inner side end of the corresponding opening on the printing template; the length of the outer side end of each opening extending out of the outer side end of the corresponding pad satisfies the following formula: 0≤X1≤X; wherein X1 is the length of the outer side end of each opening extending out of the outer side end of the corresponding pad, and X is the length of the inner side end of each pad extending out of the inner side end of the corresponding opening on the printing template.

2. The method of claim 1, wherein, The obtaining of each solder end region of the QFN device comprises: obtaining each solder end region of the QFN device through a QFN device manual.

3. The method of claim 1, wherein, The obtaining of each pad region of the PCB comprises: obtaining each pad region of the PCB through a PCB file.

4. The method of claim 1, wherein, The shape of the opening is adapted to the shape of the pad.

5. A tin bead resistant printing stencil, characterized by The printing template comprises an opening, and the opening is obtained by any one of the methods in claims 1-4.

6. The printing template of claim 5, wherein, The shape of the opening is adapted to the shape of the pad.

7. The printing template according to claim 5 or 6, characterized in that The thickness of the printing template is greater than 0.1mm.

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